Synthesis of Imidazo[1,2-f]phenanthridines by Recyclable Magnetic MOF-Catalyzed Coupling and Cyclization of 2-(2-Bromoaryl)imidazoles with Cyclohexane-1,3-diones Followed by Aromatization.

2-(2-Bromoaryl)imidazoles react with cyclohexane-1,3-diones in the presence of a catalytic amount of recyclable Fe3O4@SiO2@MOF-199 and a base to give the corresponding C-C coupled and cyclized products 6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-ones in high yields. The magnetic MOF catalyst could be easily recovered and reused four times without any significant loss of catalytic activity. The coupled and cyclized scaffolds were aromatized to imidazo[1,2-f]phenanthridines in high yields by a one-pot sequential procedure including reduction, dehydration, and oxidation. The present protocol could be applied to the synthesis of Zephycandidine A, which is known to exhibit anti-tumor activity.

Introduction

Diverse synthetic methods are well documented for the construction of polynuclear N-fused hybrid scaffolds due to their biological activities and optical properties that are not shown in each homonuclear heterocyclic compound.[1] It is known that imidazo[1,2-f]phenanthridines also exhibit such biological activities and optical properties. In contrast to synthetic methods of each homonuclear isoquinoline, quinoline, and imidazole consisting of imidazo[1,2-f]phenanthridine, several synthetic methods are reported for their trinuclear N-fused hybrid scaffolds with a limited substrate scope. It is reported that 2-phenyl-1H-imidazoles react with 1,2-dihalobenzenes to give imidazo[1,2-f]phenanthridines (three examples) via a tandem palladium-catalyzed N–H/C–H arylation (Scheme , route a).[2] Parenty and Cronin demonstrated that imidazo[1,2-f]phenanthridines (four examples) can be formed by the reaction of phenanthridine with 1,2-dibromoethane or 3-bromobutan-2-one, followed by subsequent liquid ammonia treatment and oxidation using MnO2 (Scheme , route b).[3] It is also reported that imidazole-substituted 1,1′-biphenyl is found to be oxidatively coupled in the presence of a palladium catalyst to produce imidazo[1,2-f]phenanthridine itself (Scheme , route c).[4] Imidazo[1,2-f]phenanthridine itself can also be constructed by copper-catalyzed tandem C–N and C–C coupling between 2,2′-diiodo-1,1′-biphenyl and imidazole (Scheme , route d).[5] The synthesis of imidazo[1,2-f]phenanthridines was also exemplified by the reactions of 6-aminophenanthridines with 2-haloacetaldehyde as well as 6-chlorophenanthridines with 2,2-dimethoxyethylamine for the eventual application of these scaffolds to the preparation of blue phosphorescent imidazophenanthridine iridium complexes (Scheme , routes e and f).[6,7] However, these precedents still suffer from drawbacks such as limitation of substrate scope and the requirement of an expensive palladium catalyst, contamination of residual palladiums in products, and sometimes harsh reaction conditions. As part of our continuing studies directed toward transition metal-catalyzed and transition metal-free heterocyclizations via a C–C or C–N coupling, we have developed several synthetic methods for binuclear and trinuclear N-fused hybrid scaffolds.[8] The present work started during the course of the development of an unprecedented synthetic method for polynuclear N-fused hybrid scaffolds with a broad substrate scope. This report shows a new synthetic method of imidazo[1,2-f]phenanthridines by recyclable magnetic MOF-199-catalyzed C–C coupling and cyclization of 2-(2-bromoaryl)imidazoles with cyclohexane-1,3-diones, followed by aromatization (Scheme ).

Scheme 1

Synthetic Routes for Imidazo[1,2-f]phenanthridines

Results and Discussion

Table shows several representative results for the C–C coupling and cyclization of 2-(2-bromophenyl)-4,5-diphenyl-1H-imidazole (1a) with cyclohexane-1,3-dione (2a) to produce 2,3-diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridine-8(5H)-one (3a) effectively under several reaction conditions.[9] Treatment of 1a with 2 equiv of 2a in DMF at 60 °C for 20 h in the presence of a catalytic amount of core–shell magnetic metal organic framework MOF-199 (Fe3O4@SiO2@MOF-199, 5 mol %) along with Cs2CO3 afforded 3a in only 14% yield with 46% conversion of 1a (Table , entry 1).[10] However, higher yield of 3a and complete conversion of 1a were observed by further addition of l-proline as a ligand to the system (Table , entry 2).[11] Prolonging the reaction time up to 20 h was necessary for the effective formation of 3a with complete conversion of 1a (Table , entries 2–4). Performing the reaction for 48 h at ambient reaction temperature produced 3a in only 11% yield with lower conversion of 1a (Table , entry 5). The reaction also proceeded using other amino acids such as trans-4-hydroxy-l-proline, glycine, and l-phenylalanine, but the yield of 3a was generally lower than that obtained in the presence of l-proline (Table , entries 6–8). No expected scaffold 3a was produced in the presence of 1,10-phenanthroline, instead, a considerable amount of 2,4,5-triphenyl-1H-imidazole (4) was formed by debromination of 1a (Table , entry 9). The reaction using l-cysteine as a ligand was also accompanied by the formation of 4 (Table , entry 10). It is reported that aryl bromides were debrominated to arenes by using DMF as a hydrogen source with the assistance of a base.[12] Performing the reaction under a low molar ratio of [2a]/[1a] = 1 afforded 3a and 4 in 50% and 5% yields, respectively (Table , entry 11). Among the bases examined under the employed conditions, Cs2CO3 was revealed to be the base of choice (Table , entries 2, 12–15). Other solvents such as 1,4-dioxane, toluene, and HMPA were not as effective as DMF (Table , entries 16–18). On the other hand, the reaction did not proceed at all in the absence of Fe3O4@SiO2@MOF-199 (Table , entry 19).

Table 1

Optimization of Conditionsa

						yield (%)
entry	ligand	base	solvent	time (h)	Conv. (%) of 1a	3a	4
1		Cs2CO3	DMF	20	46	14	0
2	l-proline	Cs2CO3	DMF	20	100	91	0
3	l-proline	Cs2CO3	DMF	5	76	41	0
4	l-proline	Cs2CO3	DMF	10	85	43	0
5b	l-proline	Cs2CO3	DMF	48	33	11	0
6	trans-4-hydroxy- l-proline	Cs2CO3	DMF	20	85	37	0
7	glycine	Cs2CO3	DMF	20	70	36	0
8	l-phenylalanine	Cs2CO3	DMF	20	100	64	0
9	1,10-phenanthroline	Cs2CO3	DMF	20	84	0	41
10	l-cysteine	Cs2CO3	DMF	20	67	19	13
11c	l-proline	Cs2CO3	DMF	20	94	50	5
12	l-proline	K2CO3	DMF	20	70	42	2
13	l-proline	K3PO4	DMF	20	62	38	0
14	l-proline	CsF	DMF	20	77	43	0
15	l-proline	KOtBu	DMF	20	71	37	0
16	l-proline	Cs2CO3	1,4-dioxane	20	41	37	0
17	l-proline	Cs2CO3	toluene	20	39	0	0
18	l-proline	Cs2CO3	HMPA	20	100	72	0
19d	l-proline	Cs2CO3	DMF	20	23	0	0

Reaction conditions: 1a (0.5 mmol), 2a (1 mmol), Fe3O4@SiO2@MOF-199 (0.025 mmol), ligand (0.1 mmol), base (0.5 mmol), DMF (5 mL), 60 °C.

At 25 °C.

2a (0.5 mmol).

In the absence of Fe3O4@SiO2@MOF-199.

Various 2-(2-bromoaryl)imidazoles 1 were subjected to the reaction with cyclohexane-1,3-diones 2 under the optimized reaction conditions in order to examine the scope and limitation of the reaction, and several representative results are shown in Table .[13] 2-(2-Bromophenyl)-4,5-diphenyl-1H-imidazole (1a) also readily reacted with several cyclohexane-1,3-diones 2b–d to give the corresponding coupled and cyclized products in high yields irrespective of the identity of the substituents on 2b–d. In the case of the reaction with 2c, a quantitative yield of 3c was observed with further loading of the catalyst. 2-(2-Bromoaryl)imidazoles 1b–g having electron-donating and -withdrawing substituents on the bromoaryl moiety or on the phenyl moiety attached to the imidazole ring were also coupled and cyclized with 2a to form the corresponding products 3e–j in 73–95% yields. The electronic nature of such substituents had no significant relevance with product yield. Here again, in almost all cases, further loading of the catalyst was needed for the effective formation of products. The coupling and cyclization of 2-(2-bromophenyl)-4,5-diheteroarylimidazole 1h with 2a likewise took place to give the corresponding scaffold 3k in a similar yield. The reaction of 2-(2-bromophenyl)imidazoles (1i and 1j), which have no aryl substituents or one phenyl substituent on the imidazole ring with cyclohexane-1,3-diones 2a–d, similarly proceeded to give the corresponding coupled and cyclized products in 69–93% yields.[14] However, a lower yield of 3r was observed from the reaction of 2-(2-bromovinyl)imidazole 1k and 2a.

Table 2

Scope of the Reactiona

Reaction conditions: 1 (0.5 mmol), 2 (1 mmol), Fe3O4@SiO2@MOF-199 (0.025 mmol), Cs2CO3 (0.5 mmol), l-proline (0.1 mmol), DMF (5 mL), 60 °C, 20 h.

Fe3O4@SiO2@MOF-199 (0.05 mmol).

On the other hand, the Fe3O4@SiO2@MOF-199 catalytic system could be recovered easily and reused four times without any significant loss of catalytic activity. The yield of 3a by the reaction of 1a with 2a under a similar condition (see the Supporting Information) shown in entry 2 of Table was observed from 91% (1st reuse), 89% (2nd reuse), 88% (3rd reuse), to 89% (4th reuse). X-ray diffraction (XRD) spectra of reused Fe3O4@SiO2@MOF-199 (after the fourth run) showed a similar pattern as compared to that of fresh Fe3O4@SiO2@MOF-199 (Figure ).

Figure 1

XRD spectra of (a) fresh Fe3O4@SiO2@MOF-199 and (b) reused Fe3O4@SiO2@MOF-199 (after the fourth run under the conditions shown in entry 2 of Table ).

Although the exact nature of the present reaction is still obscure, the plausible pathway seems to proceed via an initial MOF-199-catalyzed Ullmann-type C–C coupling between 1 and 2, followed by cyclocondensation.[9,15] We confirmed in a separate experiment that MOF-199 exhibited a similar catalytic activity like Fe3O4@SiO2@MOF-199. Treatment of 1a with 2a in the presence of MOF-199 under the conditions shown in entry 2 of Table afforded 3a in 92% yield. A reviewer suggested that the substrate needs to get into the holes of the MOF catalyst for Ullmann cross-coupling. It is reported that MOF-199 was used as an efficient heterogeneous catalyst for C(sp2)–C and C(sp2)–N coupling reactions, and such a heterogeneous catalysis may occur on an exposed copper site of the MOF catalyst.[16,17] To confirm the possibility on catalysis of a trace amount of CuX species leached from the solid MOF-199 catalyst, we carried out an additional experiment. As shown in entry 3 of Table , the reaction of 1a with 2a for a short reaction time (5 h) produced 3a in 41% yield with incomplete conversion of 1a. When 1a was reacted with 2a for 5 h under the employed conditions and the reaction continued for another 15 h after removing Fe3O4@SiO2@MOF-199 from the mixture, the yield of 3a hardly increased (43%). This result indicates that the present reaction can proceed in the presence of the solid MOF catalyst.

All scaffolds 3a–q shown in Table could be converted into imidazo[1,2-f]phenanthridines 5a–q by a one-pot sequential process (Table ). Initial reduction of 3a–q to alcohols with NaBH4 in MeOH/THF followed by dehydration of the produced alcohols by E2 elimination using POCl3 and pyridine and subsequent oxidation with DDQ under an O2 atmosphere afforded the corresponding aromatized products 5a–q in high yields.[18,19] In most cases, the product yield increases on prolonging the reaction time in the final oxidation stage. A similar sequential treatment of scaffold 3r under the employed conditions also gave the aromatized product 5r. However, the yield was lower than that by the reaction with almost all 3.

Table 3

Aromatization of 3 Into 5a

Reaction conditions: [1] 3 (0.2 mmol), NaBH4 (0.6 mmol), THF (1 mL), MeOH (4 mL); [2] POCl3 (1.8 mmol), pyridine (3 mL); [3] DDQ (0.6 mmol), DMF (5 mL), O2 (1 atm).

It is known that Zephycandidine A, the first naturally occurring imidazo[1,2-f]phenanthridine alkaloid isolated from Zephyranthes candida (Amaryllidaceae), exhibits significant anti-tumor and anti-acetylcholinesterase activities.[20] The present protocol could be applied to the synthesis of Zephycandidine A with three steps starting from 6-bromobenzo[d][1,3]dioxole-5-carbaldehyde (6) (Scheme ). The starting 2-(2-bromoaryl)imidazole 1l was prepared from an initial cyclization of 6 with ethylenediamine, followed by oxidation using PhI(OAc)2 in 69% yield.[21,22] The coupling and cyclocondensation product 3s (10 mol % of Fe3O4@SiO2@MOF-199) and aromatization product 5s (for 12 h, final oxidation stage) were synthesized by the present protocol in 71 and 92% yields, respectively. To the best of our knowledge, only one report has been found for the synthesis of Zephycandidine A. It is reported that Zephycandidine A can be prepared in three steps from the naturally occurring alkaloid haemanthamine.[23]

Scheme 2

Synthesis of Zephycandidine A

On the other hand, similar treatment of tetrazole 7 and triazole 10 with 2a under the employed conditions also afforded the corresponding coupled and cyclized products 8 and 11 in 34 and 37% yields, respectively (Scheme ). These products (8 and 11) were similarly aromatized to tetrazolo[1,5-f]phenanthridine (9) and 2-phenyl-[1,2,4]triazolo[1,5-f]phenanthridine (12) in 62 and 80% yields, respectively, by a one-pot sequential procedure described above (Scheme ).

Scheme 3

Synthesis of Tetrazolo- and Triazolo[1,5-f]phenanthridines

Conclusions

In summary, it has been shown that an array of imidazo[1,2-f]phenanthridines could be synthesized by recyclable Fe3O4@SiO2@MOF-199-catalyzed coupling and cyclization of 2-(2-bromoaryl)imidazoles with cyclohexane-1,3-diones, followed by aromatization. The MOF catalyst could be easily recovered by fixing with a magnet and reused four times without any significant loss of catalytic activity. The present reaction could be applicable to the synthesis of Zephycandidine A, which is known to exhibit anti-tumor activity. Further challenges on the synthesis of valuable scaffolds using this protocol are under way.

Experimental Section

General Information

1H (500 MHz) and 13C NMR (125 MHz) spectra were recorded on a Bruker Avance Digital 500 spectrometer using TMS as an internal standard in CDCl3. High-resolution mass data were obtained using electronic ionization (HRMS, magnetic sector-electric sector double focusing mass analyzer) at the Korea Basic Science Center (Daegu). XRD experiments were performed by a D8 Advance, Bruker diffractometer using a Cu source working at 40 kV and 40 mA over the range of 0–60o (2θ). Melting points were measured on a microscopic melting point apparatus (Stanford Research Inc. MPA100 automated melting point apparatus). The products were isolated by TLC (a glass plate coated with Kieselgel 60 GF254, Merck). The starting materials 1 were prepared from the corresponding aldehydes and benzils according to the reported methods.[8f,8g,13] Other commercially available organic and inorganic reagents were used without further purification.

General Procedure for the Synthesis of 3

To a 5 mL screw-capped vial, 1 (0.5 mmol), 2 (1 mmol), Fe3O4@SiO2@MOF-199 (5–10 mol %), Cs2CO3 (0.163 g, 0.5 mmol), l-proline (0.012 g, 0.1 mmol), and DMF (5 mL) were added. After stirring the reaction mixture at room temperature for 5 min, it was heated at 60 °C for 20 h under usual heating. The reaction mixture was cooled and filtered through a short silica gel column to eliminate inorganic salts using ethyl acetate. Removal of the eluent under reduced pressure left a crude mixture, which was purified by TLC (dichloromethane/MeOH = 99/1) to give 3. All new products were characterized spectroscopically as shown below.

2,3-Diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3a)[11]

3a was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.177 g, 91%); mp 214–217 °C. 1H NMR (500 MHz, CDCl3): δ 9.23–9.19 (m, 1H), 8.86–8.83 (m, 1H), 7.67–7.61 (m, 2H), 7.55–7.47 (m, 7H), 7.26–7.19 (m, 3H), 2.70–2.67 (m, 2H), 2.65–2.62 (m, 2H), 1.96–1.91 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.1, 147.1, 144.2, 143.4, 134.0, 133.0, 132.1, 129.4, 129.3, 128.8, 128.2, 128.1, 127.8, 127.4, 127.1, 126.6, 124.7, 123.7, 123.2, 116.8, 39.1, 30.2, 21.6.

6-Methyl-2,3-diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3b)[11]

3b was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.167 g, 83%); mp 224–227 °C. 1H NMR (500 MHz, CDCl3): δ 9.25–9.21 (m, 1H), 8.88–8.85 (m, 1H), 7.66–7.61 (m, 2H), 7.58–7.45 (m, 7H), 7.26–7.20 (m, 3H), 2.80–2.75 (m, 1H), 2.71–2.67 (m, 1H), 2.35–2.23 (m, 2H), 2.19–2.09 (m, 1H), 0.86 (d, J = 6.5 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.3, 146.5, 144.2, 143.2, 134.0, 133.0, 132.2, 132.1, 129.4, 129.3, 128.7, 128.6, 128.2, 128.0, 127.8, 127.4, 126.9, 126.5, 124.7, 123.7, 123.1, 116.2, 47.1, 38.0, 28.6, 20.7.

6-Isopropyl-2,3-diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3c)

3c was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.211 g, 98%); mp 184–187 °C. 1H NMR (500 MHz, CDCl3): δ 9.22–9.19 (m, 1H), 8.83–8.79 (m, 1H), 7.63–7.45 (m, 9H), 7.25–7.18 (m, 3H), 2.83–2.79 (m, 1H), 2.69–2.65 (m, 1H), 2.34–2.21 (m, 2H), 1.79–1.71 (m, 1H), 1.40–1.30 (m, 1H), 0.73 (d, J = 6.8 Hz, 3H), 0.54 (d, J = 6.8 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.6, 147.1, 144.1, 143.1, 134.0, 133.4, 132.3, 132.2, 129.3, 128.8, 128.6, 128.1, 128.0, 127.7, 127.4, 126.9, 126.4, 124.6, 123.6, 123.1, 116.0, 43.6, 39.7, 34.0, 32.0, 19.6, 18.6. HRMS (EI) m/z: [M]+ calcd for C30H26N2O, 430.2045; found, 430.2041.

2,3,6-Triphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3d)[11]

3d was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.204 g, 88%); mp 221–223 °C. 1H NMR (500 MHz, CDCl3): δ 9.25–9.22 (m, 1H), 8.81–8.79 (m, 1H), 7.62–7.57 (m, 4H), 7.51–7.44 (m, 4H), 7.40–7.37 (m, 1H), 7.23–7.16 (m, 6H), 6.86 (d, J = 7.0 Hz, 2H), 3.31–3.24 (m, 1H), 3.07–3.03 (m, 1H), 2.97–2.93 (m, 1H), 2.76–2.66 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.3, 146.5, 144.1, 143.1, 141.6, 133.9, 133.0, 132.2, 132.1, 129.4, 129.3, 128.8, 128.6 (128.62), 128.6 (128.58), 128.2, 128.0, 127.9, 127.5, 126.9, 126.8, 126.4, 126.0, 124.7, 123.6, 123.1, 116.2, 46.1, 37.9, 36.5.

10-Methyl-2,3-diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3e)[11]

3e was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.165 g, 82%); mp 212–214 °C. 1H NMR (500 MHz, CDCl3): δ 8.98 (s, 1H), 8.69 (d, J = 8.2 Hz, 1H), 7.53–7.41 (m, 8H), 7.24–7.16 (m, 3H), 2.65–2.62 (m, 2H), 2.60–2.57 (m, 2H), 2.53 (s, 3H), 1.92–1.87 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.1, 147.1, 144.3, 143.2, 139.4, 134.1, 133.0, 132.1, 129.3, 129.2, 128.7, 128.1, 128.0, 127.3, 127.1, 126.2, 124.3, 123.5, 120.9, 116.6, 39.1, 30.1, 22.3, 21.5.

10,11-Dimethoxy-2,3-diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3f)

3f was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.182 g, 81%); mp 257–260 °C. 1H NMR (500 MHz, CDCl3): δ 8.90 (s, 1H), 8.20 (s, 1H), 7.55–7.46 (m, 7H), 7.26–7.20 (m, 3H), 4.13 (s, 3H), 4.07 (s, 3H), 2.70–2.68 (m, 2H), 2.65–2.62 (m, 2H), 1.96–1.91 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.8, 151.1, 149.7, 145.8, 144.1, 143.4, 134.1, 133.0, 132.1, 129.2, 128.7, 128.2 (128.18), 128.2 (128.15), 127.4, 124.2, 122.1, 118.0, 116.0, 107.5, 103.9, 56.2, 56.0, 39.2, 30.2, 21.6. HRMS (EI) m/z: [M]+ calcd for C29H24N2O3, 448.1787; found, 448.1788.

2,3-Diphenyl-6,7-dihydro-[1,3]dioxolo[4,5-j]imidazo[1,2-f]phenanthridin-8(5H)-one (3g)

3g was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.158 g, 73%); mp 262–265 °C. 1H NMR (500 MHz, CDCl3): δ 8.73 (s, 1H), 8.18 (s, 1H), 7.53–7.46 (m, 7H), 7.26–7.19 (m, 3H), 6.10 (s, 2H), 2.67–2.65 (m, 2H), 2.62–2.59 (m, 2H), 1.94–1.89 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.3, 150.2, 148.1, 145.8, 144.3, 143.5, 134.3, 133.3, 132.3, 129.3, 128.8, 128.3, 128.2, 127.5, 124.2, 123.5, 119.6, 116.6, 105.4, 102.0, 101.7, 39.3, 30.2, 21.7. HRMS (EI) m/z: [M]+ calcd for C28H20N2O3, 432.1474; found, 432.1476.

11-Fluoro-2,3-diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3h)

3h was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.193 g, 95%); mp 240–242 °C. 1H NMR (500 MHz, CDCl3): δ 9.27 (dd, J = 9.4 and 5.6 Hz, 1H), 8.46 (dd, J = 9.2 and 2.9 Hz, 1H), 7.56–7.48 (m, 7H), 7.37–7.33 (m, 1H), 7.26–7.22 (m, 3H), 2.69–2.67 (m, 2H), 2.65–2.62 (m, 2H), 1.97–1.91 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.0, 161.8 (d, 1JC–F = 247.8 Hz), 146.5, 143.5, 143.3 (143.32), 143.3 (143.29), 133.7, 132.7, 132.0, 129.7 (d, 3JC-F = 8.1 Hz), 129.4, 128.8, 128.2, 128.0, 127.6, 125.1 (125.14), 125.1 (125.06), 125.0, 123.6 (d, 4JC–F = 2.3 Hz), 117.8 (d, 2JC–F = 22.4 Hz), 116.4, 108.7 (d, 2JC–F = 23.0 Hz), 39.0, 30.0, 21.5. HRMS (EI) m/z: [M]+ calcd for C27H19FN2O, 406.1481; found, 406.1481.

2,3-Di-p-tolyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3i)

3i was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.194 g, 93%); mp 208–210 °C. 1H NMR (500 MHz, CDCl3): δ 9.21–9.17 (m, 1H), 8.84–8.80 (m, 1H), 7.64–7.58 (m, 2H), 7.46–7.44 (m, 2H), 7.37–7.35 (m, 2H), 7.27 (d, J = 7.8 Hz, 2H), 7.05 (d, J = 8.0 Hz, 2H), 2.70–2.67 (m, 2H), 2.63–2.60 (m, 2H), 2.47 (s, 3H), 2.30 (s, 3H), 1.95–1.90 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.2, 147.3, 143.9, 143.3, 139.2, 137.1, 131.9, 131.2, 129.9, 129.5, 129.2, 128.9, 127.9, 127.7, 127.0, 126.5, 124.3, 123.6, 123.2, 116.6, 39.1, 30.1, 21.5 (21.53), 21.5 (21.49), 21.2. HRMS (EI) m/z: [M]+ calcd for C29H24N2O, 416.1889; found, 416.1886.

2,3-Bis(4-fluorophenyl)-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3j)

3j was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.197 g, 93%); mp 219–223 °C. 1H NMR (500 MHz, CDCl3): δ 9.21–9.19 (m, 1H), 8.82–8.79 (m, 1H), 7.68–7.62 (m, 2H), 7.51–7.46 (m, 4H), 7.23–7.19 (m, 2H), 6.98–6.93 (m, 2H), 2.68–2.64 (m, 4H), 2.00–1.95 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.0, 163.3 (d, 1JC–F = 249.3 Hz), 162.4 (d, 1JC–F = 246.1 Hz), 146.7, 144.3, 142.9, 133.9 (d, 3JC–F = 8.1 Hz), 129.9 (d, 4JC–F = 3.3 Hz), 129.8 (d, 3JC–F = 8.1 Hz), 129.6, 128.8 (d, 4JC–F = 3.6 Hz), 128.0, 127.1, 126.7, 123.6, 123.1 (123.14), 123.1 (123.07), 116.9, 116.1 (d, 2JC–F = 21.6 Hz), 115.2 (d, 2JC–F = 21.1 Hz), 39.0, 30.3, 21.5. HRMS (EI) m/z: [M]+ calcd for C27H18F2N2O, 424.1387; found, 424.1388.

2,3-Di(furan-2-yl)-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3k)

3k was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.155 g, 84%); mp 210–213 °C. 1H NMR (500 MHz, CDCl3): δ 9.26–9.24 (m, 1H), 8.87–8.85 (m, 1H), 7.73 (dd, J = 1.9 and 0.8 Hz, 1H), 7.71–7.63 (m, 2H), 7.50 (dd, J = 1.8 and 0.7 Hz, 1H), 6.71 (dd, J = 3.3 and 0.8 Hz, 1H), 6.64 (dd, J = 3.3 and 2.0 Hz, 1H), 6.42 (dd, J = 3.4 and 1.8 Hz, 1H), 6.36 (dd, J = 3.4 and 0.7 Hz, 1H), 2.87–2.84 (m, 2H), 2.72–2.69 (m, 2H), 2.12–2.06 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.0, 148.1, 146.4, 145.8, 143.8, 143.0, 142.8, 139.9, 130.1, 127.9, 127.6, 126.7, 124.1, 122.7, 117.1, 115.6, 112.7, 111.8, 111.4, 109.0, 39.2, 26.7, 21.3. HRMS (EI) m/z: [M]+ calcd for C23H16N2O3, 368.1161; found, 368.1162.

2-Phenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3l)

3l was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.123 g, 79%); mp 184–187 °C. 1H NMR (500 MHz, CDCl3): δ 9.28–9.27 (m, 1H), 8.73–8.71 (m, 1H), 8.00–7.98 (m, 2H), 7.73 (s, 1H), 7.65–7.59 (m, 2H), 7.46–7.43 (m, 2H), 7.36–7.33 (m, 1H), 3.17–3.15 (m, 2H), 2.78–2.76 (m, 2H), 2.37–2.32 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.7, 145.8, 144.2, 143.9, 133.4, 129.5, 128.8, 128.2, 127.8, 127.1, 126.7, 126.0, 123.4, 122.5, 115.6, 107.2, 39.4, 27.2, 20.7. HRMS (EI) m/z: [M]+ calcd for C21H16N2O, 312.1263; found, 312.1264.

2,6-Diphenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3m)

3m was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.161 g, 83%); mp 244–246 °C. 1H NMR (500 MHz, CDCl3): δ 9.28–9.26 (m, 1H), 8.70–8.68 (m, 1H), 7.94–7.92 (m, 2H), 7.63–7.57 (m, 3H), 7.45–7.30 (m, 8H), 3.68–3.61 (m, 1H), 3.37–3.33 (m, 1H), 3.20 (dd, J = 17.2 and 11.4 Hz, 1H), 3.03–2.94 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 196.9, 145.7, 144.2, 143.2, 142.0, 133.2, 129.5, 129.1, 128.8, 128.2, 127.9, 127.6, 126.9, 126.8, 126.6, 125.9, 123.4, 122.4, 115.1, 107.2, 46.0, 38.7, 35.1. HRMS (EI) m/z: [M]+ calcd for C27H20N2O, 388.1576; found, 388.1574.

6,7-Dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3n)

3n was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.100 g, 85%); mp 153–156 °C. 1H NMR (500 MHz, CDCl3): δ 9.32–9.30 (m, 1H), 8.66–8.64 (m, 1H), 7.68 (d, J = 1.5 Hz, 1H), 7.67–7.61 (m, 2H), 7.59 (d, J = 1.5 Hz, 1H), 3.21–3.19 (m, 2H), 2.81–2.78 (m, 2H), 2.39–2.34 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.9, 144.2, 144.0, 133.4, 129.5, 128.0, 126.9, 126.7, 123.1, 122.7, 115.8, 112.0, 39.4, 27.2, 20.7. HRMS (EI) m/z: [M]+ calcd for C15H12N2O, 236.0950; found, 236.0949.

6-Methyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3o)

3o was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.086 g, 69%); mp 134–137 °C. 1H NMR (500 MHz, CDCl3): δ 9.29–9.27 (m, 1H), 8.64 (d, J = 7.4 Hz, 1H), 7.66–7.59 (m, 3H), 7.54 (s, 1H), 3.21–3.16 (m, 1H), 2.81–2.73 (m, 2H), 2.58–2.44 (m, 2H), 1.27 (d, J = 6.4 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.8, 144.0, 143.6, 133.3, 129.4, 127.9, 126.9, 126.6, 123.1, 122.6, 115.3, 112.0, 47.5, 35.1, 28.2, 21.2. HRMS (EI) m/z: [M]+ calcd for C15H12N2O, 250.1106; found, 250.1103.

6-Isopropyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3p)

3p was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.093 g, 67%); mp 140–143 °C. 1H NMR (500 MHz, CDCl3): δ 9.31–9.27 (m, 1H), 8.64–8.62 (m, 1H), 7.65 (d, J = 1.3 Hz, 1H), 7.64–7.59 (m, 2H), 7.57 (d, J = 1.3 Hz, 1H), 3.17–3.12 (m, 1H), 2.88–2.79 (m, 2H), 2.52–2.47 (m, 1H), 2.23–2.16 (m, 1H), 1.84–1.75 (m, 1H), 1.08 (d, J = 7.0 Hz, 3H), 1.06 (d, J = 7.0 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 198.3, 144.0, 133.3, 129.4, 127.9, 126.8, 126.6, 123.1, 122.6, 115.3, 112.0, 43.3, 39.1, 32.0, 31.0, 19.6, 19.4. HRMS (EI) m/z: [M]+ calcd for C18H18N2O, 278.1419; found, 278.1422.

6-Phenyl-6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-one (3q)

3q was purified by TLC (dichloromethane/MeOH = 99/1) as a pale yellow solid (0.128 g, 82%); mp 216–218 °C. 1H NMR (500 MHz, CDCl3): δ 9.35–9.34 (m, 1H), 8.68–8.66 (m, 1H), 7.68–7.62 (m, 3H), 7.54 (d, J = 0.6 Hz, 1H), 7.44–7.42 (m, 2H), 7.37–7.33 (m, 3H), 3.71–3.64 (m, 1H), 3.46–3.41 (m, 1H), 3.31–3.25 (m, 1H), 3.06–2.99 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.2, 144.3, 143.6, 142.0, 133.7, 129.7, 129.3, 128.2, 127.8, 126.9, 126.8 (126.83), 126.8 (126.80), 123.3, 122.9, 115.6, 112.2, 46.2, 38.9, 35.2. HRMS (EI) m/z: [M]+ calcd for C21H16N2O, 312.1263; found, 312.1265.

2,3-Diphenyl-6,7,9,10,11,12-hexahydroimidazo[1,2-f]phenanthridin-8(5H)-one (3r)

3r was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.110 g, 56%); mp 254–256 °C. 1H NMR (500 MHz, CDCl3): δ 7.49–7.43 (m, 7H), 7.22–7.16 (m, 3H), 3.17–3.15 (m, 2H), 3.13–3.11 (m, 2H), 2.61–2.59 (m, 2H), 2.53–2.50 (m, 2H), 1.91–1.80 (m, 6H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.9, 145.8, 144.9, 144.5, 134.4, 133.8, 133.1, 132.3, 129.0, 128.4, 128.3, 128.0, 127.3, 124.9, 122.9, 120.2, 39.2, 29.7, 28.5, 25.1, 23.3, 21.6, 21.5. HRMS (EI): m/z [M+] calcd for C27H24N2O, 392.1889; found, 392.1885.

6,7-Dihydro-[1,3]dioxolo[4,5-j]imidazo[1,2-f]phenanthridin-8(5H)-one (3s)

3s was purified by TLC (dichloromethane/MeOH = 99/1) as a white solid (0.100 g, 71%); mp 237–239 °C. 1H NMR (500 MHz, CDCl3): δ 8.86 (s, 1H), 8.01 (s, 1H), 7.66 (d, J = 1.2 Hz, 1H), 7.56 (d, J = 1.1 Hz, 1H), 6.12 (s, 2H), 3.22–3.19 (m, 2H), 2.80–2.78 (m, 2H), 2.39–2.33 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.9, 150.1, 148.1, 144.2, 142.6, 133.4, 123.3, 119.0, 115.6, 111.4, 105.4, 101.7, 101.5, 39.5, 27.2, 20.7. HRMS (EI) m/z: [M]+ calcd for C16H12N2O3, 280.0848; found, 280.0846.

6,7-Dihydrotetrazolo[1,5-f]phenanthridin-8(5H)-one (8)

8 was purified by TLC (dichloromethane/MeOH = 97/3) as a white solid (0.041 g, 34%); mp 201–203 °C. 1H NMR (500 MHz, CDCl3): δ 9.44 (d, J = 8.6 Hz, 1H), 8.79 (dd, J = 8.0 and 1.0 Hz, 1H), 7.93–7.89 (m, 1H), 7.83–7.79 (m, 1H), 3.74–3.72 (m, 2H), 2.92–2.90 (m, 2H), 2.49–2.43 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.2, 148.3, 143.2, 132.8, 129.5, 129.3, 127.5, 125.1, 118.8, 118.3, 39.8, 25.8, 20.8. HRMS (EI) m/z: [M]+ calcd for C13H10N4O, 238.0855; found, 238.0856.

2-Phenyl-6,7-dihydro-[1,2,4]triazolo[1,5-f]phenanthridin-8(5H)-one (11)

11 was purified by TLC (dichloromethane/MeOH = 97/3) as a white solid (0.056 g, 37%); mp 196–198 °C. 1H NMR (500 MHz, CDCl3): δ 9.41 (d, J = 8.5 Hz, 1H), 8.67 (dd, J = 8.0 and 1.0 Hz, 1H), 8.35–8.33 (m, 2H), 7.77–7.74 (m, 1H), 7.68–7.64 (m, 1H), 7.53–7.47 (m, 3H), 3.60–3.57 (m, 2H), 2.84–2.81 (m, 2H), 2.38–2.33 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 197.8, 164.5, 151.4, 146.5, 131.3, 130.5, 130.3, 129.1, 128.7, 127.9, 127.4, 126.9, 124.3, 120.9, 115.7, 39.8, 25.9, 20.9. HRMS (EI) m/z: [M]+ calcd for C20H15N3O, 313.1215; found, 313.1212.

General Procedure for the Synthesis of 5

To 25 mL round-bottom flask were added 3 (0.2 mmol), NaBH4 (0.023 g, 0.6 mmol), and anhydrous THF/MeOH = 1/4 (5 mL). After stirring the reaction mixture at room temperature for 1 h, the solvents were removed under reduced pressure. Then, POCl3 (0.17 mL) and pyridine (3 mL) were added to the residual solid and the reaction mixture was heated at 100 °C for 1 h. Removal of solvents left a crude mixture to which were added DDQ (0.136 g, 0.6 mmol) and DMF (5 mL), and then, the reaction mixture was stirred and heated at 110 °C for 2–12 h. After removing the solvent, the crude mixture was filtered through a short silica gel column using chloroform and was purified by TLC (dichloromethane/MeOH = 200/1) to give 5.

2,3-Diphenylimidazo[1,2-f]phenanthridine (5a)[24]

5a was purified by TLC (dichloromethane/MeOH = 200/1) as a pale yellow solid (0.060 g, 81%); mp 175–178 °C. 1H NMR (500 MHz, CDCl3): δ 8.88–8.85 (m, 1H), 8.45 (dd, J = 8.2 and 1.4 Hz, 1H), 8.38–8.35 (m, 1H), 7.68–7.63 (m, 2H), 7.60–7.53 (m, 7H), 7.40–7.36 (m, 1H), 7.30–7.23 (m, 3H), 7.22–7.15 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.6, 141.3, 134.5, 133.5, 133.2, 131.7, 129.6, 129.3, 128.6, 128.5, 128.1, 127.9, 127.8, 127.7, 126.9, 125.4, 124.7, 124.5, 124.1, 123.9, 122.8, 122.1, 117.6.

6-Methyl-2,3-diphenylimidazo[1,2-f]phenanthridine (5b)

5b was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.072 g, 94%); mp 185–187 °C. 1H NMR (500 MHz, CDCl3): δ 8.86–8.82 (m, 1H), 8.32–8.28 (m, 2H), 7.64–7.53 (m, 9H), 7.27–7.24 (m, 2H), 7.22–7.17 (m, 2H), 6.98 (s, 1H), 2.10 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.8, 141.1, 138.1, 134.7, 133.5, 131.8, 129.6, 129.3, 128.7, 128.3, 128.1, 128.0 (127.98), 128.0 (127.96), 127.0, 125.8, 125.4, 124.7, 123.9, 123.7, 122.0, 120.4, 118.3, 21.7. HRMS (EI): m/z [M+] calcd for C28H20N2, 384.1626; found, 384.1625.

6-Isopropyl-2,3-diphenylimidazo[1,2-f]phenanthridine (5c)

5c was purified by TLC (dichloromethane/MeOH = 200/1) as a pale yellow solid (0.081 g, 98%); mp 187–189 °C. 1H NMR (500 MHz, CDCl3): δ 8.86–8.82 (m, 1H), 8.32–8.30 (m, 2H), 7.64–7.57 (m, 9H), 7.27–7.18 (m, 5H), 2.69 (sept, J = 6.9 Hz, 1H), 0.94 (d, J = 6.9 Hz, 6H). 13C{1H} NMR (125 MHz, CDCl3): δ 149.0, 142.7, 141.0, 134.6, 133.6 (133.64), 133.6 (133.57), 131.8, 129.6, 129.2, 128.6, 128.1, 128.0, 127.9, 127.8, 126.9, 125.3, 124.6, 123.8 (123.83), 123.8 (123.82), 123.6, 121.9, 120.6, 115.2, 33.8, 23.3. HRMS (EI) m/z: [M]+ calcd for C30H24N2, 412.1939; found, 412.1940.

2,3,6-Triphenylimidazo[1,2-f]phenanthridine (5d)

5d was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.079 g, 88%); mp 272–275 °C. 1H NMR (500 MHz, CDCl3): δ 8.89–8.86 (m, 1H), 8.49 (d, J = 8.5 Hz, 1H), 8.40–8.37 (m, 1H), 7.69–7.63 (m, 11H), 7.34–7.26 (m, 5H), 7.23–7.18 (m, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.7, 141.2, 139.9, 139.3, 134.5, 133.8, 133.6, 131.7, 129.9, 129.2, 128.7, 128.5, 128.2, 127.8, 127.6, 127.0, 126.7, 125.4, 124.7, 124.5, 123.9, 122.9, 122.1, 121.8, 116.1. HRMS (EI) m/z: [M]+ calcd for C33H22N2, 446.1787; found, 446.1784.

10-Methyl-2,3-diphenylimidazo[1,2-f]phenanthridine (5e)[24]

5e was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.075 g, 97%); mp 228–230 °C. 1H NMR (500 MHz, CDCl3): δ 8.74 (d, J = 8.1 Hz, 1H), 8.43 (dd, J = 8.2 and 1.4 Hz, 1H), 8.15 (d, J = 0.5 Hz, 1H), 7.59–7.53 (m, 7H), 7.49 (dd, J = 8.2 and 1.0 Hz, 1H), 7.37–7.34 (m, 1H), 7.28–7.23 (m, 3H), 7.21–7.17 (m, 1H), 7.16–7.12 (m, 1H), 2.59 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.8, 141.2, 138.6, 134.6, 133.5, 133.3, 132.7, 129.9, 129.5, 129.2, 128.1, 127.9, 127.7, 127.6, 126.9, 125.1, 124.6, 124.4, 124.0, 122.8, 122.1, 121.6, 117.6, 22.09.

10,11-Dimethoxy-2,3-diphenylimidazo[1,2-f]phenanthridine (5f)

5f was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.071 g, 82%); mp 160–163 °C. 1H NMR (500 MHz, CDCl3): δ 8.28 (dd, J = 8.3 and 1.2 Hz, 1H), 8.22 (s, 1H), 7.69 (s, 1H), 7.60–7.53 (m, 7H), 7.37–7.34 (m, 1H), 7.29–7.23 (m, 3H), 7.21–7.18 (m, 1H), 7.13–7.09 (m, 1H), 4.14 (s, 3H), 4.09 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 150.8, 150.7, 142.6, 141.2, 134.8, 133.5, 133.0, 131.9, 129.6, 129.3, 128.2, 128.1 (128.11), 128.1 (128.08), 127.0, 126.9, 125.1, 124.4, 123.6, 122.8, 122.0, 118.5, 117.7, 105.6, 103.7, 56.5, 56.2. HRMS (EI) m/z: [M]+ calcd for C29H22N2O2, 430.1681; found, 430.1681.

2,3-Diphenyl-[1,3]dioxolo[4,5-j]imidazo[1,2-f]phenanthridine (5g)

5g was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.071 g, 85%); mp 269–272 °C. 1H NMR (500 MHz, CDCl3): δ 8.24–8.23 (m, 2H), 7.72 (s, 1H), 7.58–7.53 (m, 7H), 7.36–7.33 (m, 1H), 7.28–7.18 (m, 4H), 7.13–7.10 (m, 1H), 6.14 (s, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 149.6, 148.8, 142.7, 141.1, 134.6, 133.3, 132.9, 131.7, 129.6, 129.2, 128.1, 127.9, 127.0, 126.9, 124.8, 124.4, 123.7, 123.6, 122.8, 119.8, 117.5, 103.3, 101.7, 101.1. HRMS (EI) m/z: [M]+ calcd for C28H18N2O2, 414.1368; found, 414.1367.

11-Fluoro-2,3-diphenylimidazo[1,2-f]phenanthridine (5H)

5h was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.066 g, 85%); mp 184–186 °C. 1H NMR (500 MHz, CDCl3): δ 8.50 (dd, J = 9.3 and 2.8 Hz, 1H), 8.38–8.33 (m, 2H), 7.59–7.53 (m, 7H), 7.40–7.34 (m, 2H), 7.29–7.14 (m, 5H). 13C{1H} NMR (125 MHz, CDCl3): δ 162.7 (d, 1JC–F = 246.7 Hz), 141.7 (d, 4JC–F = 3.5 Hz), 141.5, 134.3, 133.0 (d, 3JC–F = 10.7 Hz), 131.6, 129.6, 129.4, 128.2, 127.8, 127.7, 127.1, 125.8, 125.7 (125.73), 125.7 (125.68), 124.8, 124.7 (d, 3JC–F = 8.7 Hz), 124.1 (124.14), 124.1 (124.13), 123.9, 122.3, 117.7, 116.9 (d, 2JC–F = 23.4 Hz), 110.0 (d, 2JC–F = 23.4 Hz). HRMS (EI) m/z: [M]+ calcd for C27H17FN2, 388.1376; found, 388.1373.

2,3-Di-p-tolylimidazo[1,2-f]phenanthridine (5i)

5i was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.075 g, 94%); mp 185–187 °C. 1H NMR (500 MHz, CDCl3): δ 8.86–8.84 (m, 1H), 8.43–8.41 (m, 1H), 8.35–8.33 (m, 1H), 7.66–7.60 (m, 2H), 7.50 (d, J = 8.2 Hz, 2H), 7.41–7.33 (m, 6H), 7.18–7.15 (m, 1H), 7.07 (d, J = 8.0 Hz, 2H), 2.51 (s, 3H), 2.30 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.3, 141.3, 139.1, 136.5, 133.6, 131.7, 131.5, 130.3, 130.2, 128.8, 128.5, 128.4, 127.8, 127.7, 127.6, 125.1, 124.6, 124.4, 124.0 (124.00), 124.0 (123.97), 122.7, 122.1, 117.6, 21.6, 21.2. HRMS (EI) m/z: [M]+ calcd for C29H22N2, 398.1783; found, 398.1781.

2,3-Bis(4-fluorophenyl)imidazo[1,2-f]phenanthridine (5j)

5j was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.070 g, 86%); mp 205–207 °C. 1H NMR (500 MHz, CDCl3): δ 8.85–8.82 (m, 1H), 8.47 (dd, J = 8.2 and 1.3 Hz, 1H), 8.39–8.36 (m, 1H), 7.69–7.64 (m, 2H), 7.55–7.49 (m, 4H), 7.43–7.39 (m, 1H), 7.30–7.25 (m, 3H), 7.23–7.19 (m, 1H), 6.99–6.94 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 163.4 (d, 1JC–F = 248.5 Hz), 162.2 (d, 1JC–F = 245.3 Hz), 142.7, 140.9, 133.5 (d, 3JC–F = 8.1 Hz), 133.3, 130.5 (d, 4JC–F = 3.1 Hz), 129.6 (d, 3JC–F = 7.9 Hz), 129.0 (d, 4JC–F = 3.5 Hz), 128.8, 128.6, 127.9, 127.7, 124.7 (124.74), 124.7 (124.66), 124.3, 123.9, 123.8, 122.9, 122.2, 117.3, 116.9 (d, 2JC–F = 21.5 Hz), 115.1 (d, 2JC–F = 21.3 Hz). HRMS (EI) m/z: [M]+ calcd for C27H16FN2, 406.1282; found, 406.1280.

2,3-Di(furan-2-yl)imidazo[1,2-f]phenanthridine (5k)

5k was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.061 g, 87%); mp 194–196 °C. 1H NMR (500 MHz, CDCl3): δ 8.88–8.85 (m, 1H), 8.44 (dd, J = 8.2 and 1.4 Hz, 1H), 8.37–8.34 (m, 1H), 7.79 (dd, J = 2.0 and 0.7 Hz, 1H), 7.67–7.64 (m, 2H), 7.50 (dd, J = 1.7 and 0.8 Hz, 1H), 7.45–7.42 (m, 1H), 7.36–7.33 (m, 1H), 7.00 (dd, J = 8.6 and 0.9 Hz, 1H), 6.77 (dd, J = 3.3 and 0.8 Hz, 1H), 6.72 (dd, J = 3.3 and 2.0 Hz, 1H), 6.42 (dd, J = 3.4 and 1.8 Hz, 1H), 6.38 (dd, J = 3.4 and 0.7 Hz, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 148.6, 144.1, 144.0, 143.4, 142.5, 138.0, 132.7, 129.3, 128.6, 128.5, 128.1, 125.1 (125.11), 125.1 (125.05), 124.0, 123.3, 122.6, 122.1, 116.7, 114.4, 113.6, 112.1, 111.2, 107.8. HRMS (EI) m/z: [M]+ calcd for C23H14N2O2, 350.1055; found, 350.1059.

2-Phenylimidazo[1,2-f]phenanthridine (5l)[25]

5l was purified by TLC (dichloromethane/MeOH = 200/1) as a pale red solid (0.051 g, 86%); mp 146–148 °C. 1H NMR (500 MHz, CDCl3): δ 8.79–8.77 (m, 1H), 8.48–8.46 (m, 1H), 8.39–8.37 (m, 1H), 8.25 (s, 1H), 8.07–8.05 (m, 2H), 7.91 (dd, J = 8.3 and 1.0 Hz, 1H), 7.68–7.62 (m, 3H), 7.53–7.46 (m, 3H), 7.36–7.32 (m, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 144.2, 142.8, 134.0, 131.8, 128.9, 128.7 (128.74), 128.7 (128.66), 128.5, 127.6, 125.8, 125.1, 124.5, 124.3, 123.7, 122.4, 121.9, 115.8, 107.6. HRMS (EI) m/z: [M]+ calcd for C21H14N2, 294.1157; found, 294.1154.

2,6-Diphenylimidazo[1,2-f]phenanthridine (5m)

5m was purified by TLC (dichloromethane/MeOH = 200/1) as a pale yellow solid (0.070 g, 94%); mp 147–150 °C. 1H NMR (500 MHz, CDCl3): δ 8.76–8.72 (m, 1H), 8.42 (d, J = 8.5 Hz, 1H), 8.33–8.30 (m, 1H), 8.25 (s, 1H), 8.06–8.04 (m, 2H), 8.0 (d, J = 1.7 Hz, 1H), 7.74–7.72 (m, 2H), 7.68 (dd, J = 8.4 and 1.8 Hz, 1H), 7.65–7.60 (m, 2H), 7.54–7.51 (m, 2H), 7.48–7.43 (m, 3H), 7.35–7.32 (m, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 144.2, 142.9, 141.9, 139.9, 134.0, 132.0, 129.1, 128.7 (128.72), 128.7 (128.67), 128.4, 128.2, 127.6, 127.4, 127.3, 125.8, 124.6, 124.5, 124.0, 123.6, 122.3, 120.7, 114.0, 107.6. HRMS (EI) m/z: [M]+ calcd for C27H18N2, 370.1470; found, 370.1472.

Imidazo[1,2-f]phenanthridine (5n)[26]

5n was purified by TLC (dichloromethane/MeOH = 200/1) as a pale yellow solid (0.031 g, 70%); mp 120–122 °C. 1H NMR (500 MHz, CDCl3): δ 8.70–8.66 (m, 1H), 8.49 (d, J = 7 Hz, 1H), 8.42–8.39 (m, 1H), 8.01 (d, J = 1.3 Hz, 1H), 7.90 (d, J = 7.5 Hz, 1H), 7.68–7.63 (m, 3H), 7.62 (d, J = 1.3 Hz, 1H), 7.56–7.52 (m, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.6, 131.7, 131.6, 128.7, 128.5 (128.54), 128.5 (128.46), 128.3, 127.4, 125.1, 124.1, 123.6, 122.2, 121.7, 115.6, 112.1.

6-Methylimidazo[1,2-f]phenanthridine (5o)[2]

5o was purified by TLC (dichloromethane/MeOH = 200/1) as a pale yellow solid (0.041 g, 89%); mp 129–131 °C. 1H NMR (500 MHz, CDCl3): δ 8.65–8.62 (m, 1H), 8.33–8.28 (m, 2H), 7.95 (d, J = 1.4 Hz, 1H), 7.63–7.59 (m, 4H), 7.30 (dd, J = 8.3 and 1.0 Hz, 1H), 2.55 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.7, 139.3, 131.8, 131.4, 128.6, 128.1, 127.6, 126.4, 124.2, 124.0, 123.3, 122.1, 119.4, 116.0, 111.9, 21.7.

6-Isopropylimidazo[1,2-f]phenanthridine (5p)

5p was purified by TLC (dichloromethane/MeOH = 200/1) as a pale yellow solid (0.049 g, 94%); mp 119–121 °C. 1H NMR (500 MHz, CDCl3): δ 8.67–8.64 (m, 1H), 8.40 (d, J = 8.4 Hz, 1H), 8.38–8.35 (m, 1H), 8.03 (d, J = 1.3 Hz, 1H), 7.71 (d, J = 1.6 Hz, 1H), 7.65–7.62 (m, 3H), 7.42 (dd, J = 8.4 and 1.6 Hz, 1H), 3.14 (sept, J = 6.9 Hz, 1H), 1.39 (d, J = 6.9 Hz, 6H). 13C{1H} NMR (125 MHz, CDCl3): δ 150.4, 131.9, 131.5, 128.6, 128.1, 127.7, 124.3, 124.2, 123.8, 123.4, 122.2, 119.8, 113.5, 111.9, 34.3, 24.0. HRMS (EI) m/z: [M]+ calcd for C18H16N2, 260.1313; found, 260.1315.

6-Phenylimidazo[1,2-f]phenanthridine (5q)

5q was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.056 g, 95%); mp 159–161 °C. 1H NMR (500 MHz, CDCl3): δ 8.03 (d, J = 1.3 Hz, 1H), 8.00 (d, J = 1.7 Hz, 1H), 8.66–8.64 (m, 1H), 8.46 (d, J = 8.5 Hz, 1H), 8.36–8.34 (m, 1H), 7.72–7.70 (m, 3H), 7.65–7.60 (m, 3H), 7.54–7.51 (m, 2H), 7.46–7.43 (m, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 142.7, 142.0, 139.9, 132.2, 131.7, 129.1, 128.9, 128.7, 128.5, 128.2, 127.3, 124.7, 124.2, 124.1, 123.7, 122.4, 120.8, 114.1, 112.0. HRMS (EI) m/z: [M]+ calcd for C21H14N2, 294.1157; found, 294.1155.

2,3-Diphenyl-9,10,11,12-tetrahydroimidazo[1,2-f]phenanthridine (5r)

5r was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.055 g, 74%); mp 149–152 °C. 1H NMR (500 MHz, CDCl3): δ 7.87 (dd, J = 8.2 and 1.3 Hz, 1H), 7.57–7.49 (m, 7H), 7.34–7.30 (m, 1H), 7.27 (dd, J = 8.7 and 0.8 Hz, 1H), 7.24–7.21 (m, 2H), 7.19–7.15 (m, 1H), 7.13–7.09 (m, 1H), 3.24–3.22 (m, 2H), 3.00–2.98 (m, 2H), 2.05–1.94 (m, 4H). 13C{1H} NMR (125 MHz, CDCl3): δ 144.3, 141.4, 134.8, 133.5, 133.0, 131.7, 129.5 (129.51), 129.5 (129.49), 129.1, 128.1, 128.0, 126.8, 126.4, 125.5, 125.2, 124.3, 124.1, 123.9, 116.7, 25.4, 25.0, 22.8, 22.0. HRMS (EI) m/z: [M]+ calcd for C27H22N2, 374.1783; found, 374.1785.

[1,3]Dioxolo[4,5-j]imidazo[1,2-f]phenanthridine (5s)[23]

5s was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.048 g, 92%); mp 215–217 °C. 1H NMR (500 MHz, CDCl3): δ 8.29 (dd, J = 8.2 and 1.2 Hz, 1H), 8.05 (s, 1H), 7.97 (d, J = 1.4 Hz, 1H), 7.88 (dd, J = 8.3 and 1.0 Hz, 1H), 7.76 (s, 1H), 7.61–7.59 (m, 1H), 7.58 (d, J = 1.4 Hz, 1H), 7.53–7.49 (m, 1H), 6.14 (s, 2H). 13C{1H} NMR (125 MHz, CDCl3): δ 149.5, 148.9, 131.4, 128.1, 125.0, 123.9, 123.5, 121.9, 119.7, 115.9, 111.5, 103.0, 101.8, 101.4. HRMS (EI) m/z: [M]+ calcd for C16H10N2O2, 262.0742; found, 262.0740.

Tetrazolo[1,5-f]phenanthridine (9)

9 was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.030 g, 68%); mp 225–227 °C. 1H NMR (500 MHz, CDCl3) 8.78 (d, J = 7.9 Hz, 1H), 8.69 (d, J = 8.1 Hz, 1H), 8.54–8.50 (m, 2H), 7.92–7.89 (m, 1H), 7.83–7.79 (m, 2H), 7.77–7.73 (m, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 147.3, 132.0, 130.2, 129.9, 129.5, 129.4, 128.2, 126.2, 124.0, 123.1, 122.4, 118.8, 117.7. HRMS (EI) m/z: [M]+ calcd for C13H8N4, 220.0749; found, 220.0751.

2-Phenyl-[1,2,4]triazolo[1,5-f]phenanthridine (12)

12 was purified by TLC (dichloromethane/MeOH = 200/1) as a white solid (0.0473 g, 80%); mp 188–191 °C. 1H NMR (500 MHz, CDCl3): δ 8.76–8.74 (m, 1H), 8.63–8.61 (m, 1H), 8.51–8.48 (m, 2H), 8.43–8.41 (m, 2H), 7.81–7.72 (m, 3H), 7.62–7.59 (m, 1H), 7.55–7.52 (m, 2H), 7.50–7.47 (m, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 163.0, 149.3, 132.4, 131.1, 130.3, 129.7, 129.5, 129.3, 128.7, 128.6, 127.2, 125.9, 125.4, 123.6, 122.7, 121.7, 121.5, 116.9. HRMS (EI) m/z: [M]+ calcd for C20H13N3, 295.1109; found, 295.1106.